Gun violence, when most Americans imagine it, is what happens when one person shoots another. We picture turf wars between gangs, abusive husbands turning on their wives, armed robbers punishing their victims, mass murderers opening fire on defenseless people. When we talk about how to reduce gun violence in America, what we overwhelmingly think about is preventing murder.

But murder is not the kind of gun violence that kills the most Americans.

In 2010, the last year for which complete numbers are available, the number of gun deaths by suicide in the United States outnumbered homicides 19,392 to 11,078. If you add up all American gun deaths that year, including accidents, 3 out of 5 people who died from gunshot wounds took their own lives. Those figures are not an anomaly: With just a few exceptions, the majority of gun deaths in the United States have been self-inflicted every year since at least 1920. This is a startling fact, and one that forces us to realize that, no matter what we may believe about the Second Amendment, the debate over how to reduce the death toll from guns is, to a great extent, a debate about suicide prevention.

“A lot of people, when they think about guns and violence—suicide is just kind of off the radar screen,” said Daniel Webster, the director of the Center for Gun Policy and Research at Johns Hopkins University. Webster added: “People think about the gun problem as something that someone else is going to do to them.”

With President Obama’s call for tighter gun laws working its way through Washington, and a national debate over gun rights underway, public health researchers around the country are making the argument that the issue of suicide should be a much larger part of the discussion. To reduce gun deaths as they really happen, they say, will mean not just fighting crime or keeping firearms out of the hands of potential killers, but trying to minimize the number of people who have access to guns during their darkest hours.

At the heart of this argument is the idea that the vast majority of people who have committed suicide by shooting themselves would have stayed alive if they had not been easily able to pick up a gun. This can be a difficult premise to process. First, it goes against a common intuition about suicide: that someone who wants to end his or her life will find a way to do it by any means necessary. Second, it presents a destabilizing challenge to both sides of the gun control debate, which have traditionally drawn their emotional power from people’s fear of murder.

But if the reckoning our country has been engaged in since the Newtown tragedy is driven primarily by a desire to save lives, experts say, it’s time to recognize that in the majority of cases, the people doing the shooting are also the ones who are dying.

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For Cathy Barber, a researcher at the Harvard School of Public Health, suicide became a priority in 1999, while she was engaged in a dark, emotionally draining task related to a research project on violent death. The project centered on a massive database tracking the circumstances under which people are killed, and Barber was reading through thumbnail summaries of violent deaths—thousands of them—that had taken place around the country.

At the time, her work focused on homicide and domestic abuse. But as she looked at the stories she and her team had collected, she realized that when it came to gun deaths, she was reading mostly about people who had taken their own lives. “The stories were so filled with despair and misery, but the seeds of hope were in them, too,” Barber said. “I kept thinking, ‘So many of these seem preventable.’”

Today Barber directs a suicide-prevention campaign at Harvard called Means Matter, intended to promote the notion that how people commit suicide is just as important as why—and that making it harder for suicidal people to get access to guns is a relatively simple way to save their lives.

The figures are stark. According to the National Center for Health Statistics, more people kill themselves with guns than with all other methods combined. One study found that in a group of adolescents in Pittsburgh who died by committing suicide, 72 percent lived in households with guns; among adolescents who attempted suicide but survived, that number was 37 percent. Another found that across the United States, people who committed suicide in a given year were 17 times as likely to have lived in homes with guns as people who did not. Another found that the 238,292 people in California who bought a gun in 1991 committed suicide at more than four times the rate of the general population.

At a summit on gun violence held at Johns Hopkins this past week, Harvard professor Matthew Miller presented a comparison of people living in “high-gun states,” where there are firearms in approximately 50 percent of homes, with those living in “low-gun states,” where that number is around 15 percent. Looking at these two groups of people side by side, Miller showed that they had similar rates of depression and suicidal thoughts, as well as similar rates of suicide that did not involve firearms, like hanging and poisoning. But the number of people who died by shooting themselves was almost four times greater in the high-gun states. In total, there were almost twice as many suicides among people living in high-gun states as there were in low-gun states.

Based on these and other similar studies, public health researchers have rallied around a striking conclusion: Merely having a gun in one’s home increases the likelihood that someone living there will commit suicide by a factor of two to ten, depending on age and how the gun is stored.

This is, on its face, a perplexing idea. It also has a few detractors, such as criminologist Gary Kleck of Florida State University, who has questioned the methods of public health researchers, and argued that they are not taking into account the possibility that gun-owners are more likely to commit suicide for reasons that have nothing to do with their access to guns. (“He’s just plain wrong about this,” said Miller in an e-mail. “In fact, we do know that gun owners and their families are not more suicidal, in general, than are non-gun-owners and their families.”)

In the public-health community, researchers have widely come to regard it as a basic truth that access to a gun makes it more likely that someone who wants to commit suicide actually manages to do so. A big part of the reason is simply the lethality of guns: Studies show that between 85 and 90 percent of people who shoot themselves die as a result, while the percentage of people who die using other means is vastly lower. Alan Berman, executive director of the American Association of Suicidology, points out that guns, unlike other methods, leave people no time to change their minds. They also require less preparation and planning, provided they’re accessible.

“To some people, it’s just totally counterintuitive, because it’s so obvious that if you want to kill yourself, you can always find something else to kill yourself with,” said Barber. “What they assume is that once you’re suicidal, you remain suicidal.” But a preponderance of evidence, including interviews with suicide survivors, indicates that most suicidal acts come during a surprisingly short period during which the person is suffering an acute crisis.

“When you ask people who’ve made attempts and survived,” Miller said, “even attempts that are life threatening and would have proved lethal [without emergency medical care], what they say is, ‘It was an impulsive act, and I’m glad that I’m alive.’”

The central insight for public health researchers is that a lot of lives could be saved simply by making sure that people don’t have access to an extremely lethal weapon during that high-risk period. One striking illustration of this principle can be seen in the experience of the Israeli Defense Forces, which saw a 40 percent drop in suicides after a new rule was introduced forbidding soldiers from taking their guns home with them over the weekend. Though some soldiers may have tried to kill themselves using some less lethal method instead, it appears that scores of lives were saved.

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In the months since the shootings in Newtown and Aurora, Colo., the debate over how to reduce gun violence in the United States has centered on improving background checks and imposing restrictions against assault weapons. But public health researchers focused on suicide prevention tend to take a different tack. “I don’t work on gun control issues,” said Cathy Barber. “It’s fine with me that other people do....But a third or more of people in the United States have a gun at home, and they’re valuable to them, and it doesn’t seem useful to me to ostracize them for their decisions....It just seems more useful to say, ‘OK, that’s what we’re dealing with.’”

One thing that reduces the likelihood that people will impulsively shoot themselves, public health researchers have found, is mandatory gun locks and proper gun storage, which increase the amount of time that passes after a person decides to commit suicide and actually has a loaded gun in hand. “Every minute you can delay them increases the chance that they might survive,” said David Litts, the executive secretary of the National Action Alliance for Suicide Prevention.

Another avenue that’s been identified is what’s known among public health researchers as the social norms approach. David Hemenway, director of the Harvard Injury Control Research Center and author of “Private Guns, Public Health,” sees a parallel in the successful antidrunk-driving campaigns of the 1980s and ’90s (“Friends don’t let friends drive drunk”). Lives could be saved, he believes, if it was considered socially acceptable, when a friend or family member is dealing with some serious stress in life—like job loss or divorce—to ask them to get rid of their guns temporarily.

Working with a group called the New Hampshire Firearm Safety Coalition, researchers at Harvard have started trying to promote this kind of thinking by convincing owners of gun shops in New Hampshire to distribute materials asking customers to be attentive to signs of emotional distress among their fellow gun owners, and to consider taking their guns away when they’re having a particularly hard time. “It’s a caring message—it’s not an antigun message,” said Barber. “What I’m hoping is it lights a spark—what I’d love to see is five years from now...the 11th commandment of firearm safety is, ‘If a loved one is at risk for suicide, keep firearms away from them.’”

Does such a campaign have a place in the current debate over how to stop gun violence? According to Josh Sugarmann, executive director of the Violence Policy Center, a group that promotes stricter gun control laws, it should, but doesn’t—and that on more than one occasion he has heard people say that when it comes to tallying gun deaths, “suicides don’t count.”

“It’s remarkable how many people discount suicide, as if there’s nothing that can be done about it,” said John Rosenthal, the Boston developer behind the group Stop Handgun Violence, which funds the antigun billboard on the Mass. Pike. He cited one study suggesting that the vast majority of firearm suicides among youth are committed with guns owned by a family member. “Talk about low-hanging fruit.”

But for most people, the possibility that someone they love or they themselves will die by suicide feels much more remote, and less urgent, than the risk of getting shot by an armed robber or a mass murderer like Adam Lanza. As Garen Wintemute, a public health researcher specializing in firearm violence at University of California-Davis, said, “The debate is focused around the threats that people see to themselves, and that only makes sense.”

Yet it’s important not to lose sight of the fact that, even though large-scale atrocities like Newtown are the ones that force us to confront gun violence as a nation, the opportunity to save lives may be greatest in the steady drip of private tragedies that take place every day—one by one, and out of the public eye.

“The whole point is you’ve got innocent people getting killed either way,” said Berman. “These are people who could be helped.”

Correction: Because of incorrect information provided to the Globe, an earlier version of a graphic with this story misidentified the relative rates of gun ownership in New Hampshire and Iowa. New Hampshire is not a low-gun state; Iowa is not a high-gun state.

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